Lead-Free Piezoelectric Freestanding Films with Sheet Geometry-Enhanced High-Field Piezoelectric Coefficients
(Na0.5K0.5)NbO3-based materials are promising lead-free piezoelectrics because of their relatively high Curie temperatures and piezoelectric coefficients. Using precursor powders made by a coating method, (Na0.5K0.5)0.945Li0.055Nb0.96Sb0.04O3 thick films were successfully fabricated by pressureless sintering. Large high-field −d31 value of 1700 pm/V, >20 times larger than that of the bulk counterpart, was observed at an applied dc electric field of 6–8 kV/cm. In situ X-ray diffraction study showed that the large piezoelectric response was partially due to non-180° domain switching under the electric field. Further investigation is needed to elucidate this enhancement effect. The enhanced high-field piezoelectric property observed should encourage the use of lead-free piezoelectrics.
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